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Hydro-mechanical behavior of lime-treated/untreated soils under the effects of salinity and wetting-drying cycles

Abstract : Lime treatment can enhance the workability and hydro-mechanical properties of soil through different physical-chemical reactions, such as cations exchange and pozzolanic reaction. The effectiveness of lime treatment is expected to be water chemistry and climate dependent. To understand the effects of water chemistry and climate on lime-treated soils, the project DIGUE 2020 was set up involving a dike constructed at les Salin-de-Giraud using local saline soils. In this PhD study, a laboratory work was conducted on the soils taken from Salin-de-Giraud with and without lime treatment, with emphasis put on the effects of salinity and wetting-drying cycles.In order to well characterize the salinity effect, new methods were proposed to determine the dissolved salinity and the induced osmotic suction for unsaturated soils with consideration of dissolved and precipitated salts. The mechanisms of salinity effect on the liquid limit and compaction behaviour of untreated soil, and of the drying effect on the microstructure of compacted saline soil were clarified. The optimum lime content of soil mixed with deionized water, synthetic seawater, mixed salts solution were determined by pH method. Results showed that the optimum lime content increased with the increase of salt concentration, which can be attributed to the consumption of OH- ions by Mg2+ and Ca2+ ions in the salt solution, producing the precipitations of Mg(OH)2 and CaCO3 in the alkaline environment.The effects of salinity and aggregate size on the mineralogy, microstructure and water retention property of lime-treated saline soil were investigated. Results showed that there was no cementitious compounds detecting on X-ray diffraction pattern even after a curing time as long as 150 days, due to its low quantity and poorly crystallized or amorphous phase. As a result, the microstructure of lime-treated soil varied slight during curing. The matric suction of lime-treated specimens increased significantly during curing, while the total suction increased slightly. Both total and matric suctions of lime-treated specimens increased as salinity increased. The lime-treated specimens with larger aggregates exhibited a larger modal size and thus had a smaller air entry value.The mechanical behaviour and durability of lime-treated soils were investigated by performing mercury intrusion porosimetry, bender element and oedometer tests on untreated/lime-treated specimens and the specimens subjected to wetting-drying cycles. The lime-treated specimens, as compared to untreated specimens, exhibited higher resistance to wetting-drying cycles, with the pore size distributions keeping almost reversible. The wetting-drying cycles led to reversible changes of small stain shear modulus (Gmax) and an increase of soil compressibility. The synthetic seawater, compared to deionized water, resulted in higher Gmax and higher compressibility for lime-treated soil. After wetting-drying cycles, the lime-treated specimens with lager aggregates (Dmax = 5 mm) exhibited higher yield stress and lower compressibility than the lime-treated specimens with smaller aggregates (Dmax = 0.4 mm)
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Zi Ying. Hydro-mechanical behavior of lime-treated/untreated soils under the effects of salinity and wetting-drying cycles. Géotechnique. École des Ponts ParisTech, 2021. English. ⟨NNT : 2021ENPC0019⟩. ⟨tel-03467855⟩

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